1. Field of the Invention
The invention relates to electrical discharge machining and refers more specifically to a circuit for and method of electrical discharge machining including means for rapidly switching electric current between a workpiece and electrode on and off at different selected frequencies with a minimum amount of energy dissipation, means for monitoring the voltage between the electrode and workpiece and preventing switching on of the current between the electrode and workpiece only if a short is indicated between the electrode and workpiece at the end of a machining cycle, and means for providing a trial machining cycle periodically at progressively larger intervals up to a maximum interval and resuming normal machining cycles only in response to the voltage between the electrode and workpiece reaching a proper machining magnitude.
2. Description of the Prior Art
In the past electrical discharge machining apparatus has included resistance-capacitance circuits, direct current circuits pulsed by mechanical circuit breakers and the like and some pulsed semiconductor circuits for periodically providing a spark or arc discharge between an electrode and workpiece to effect electrical machining in the presence of diaelectric fluid or coolant.
In addition, in prior electrical discharge machining circuits a short between the electrode and workpiece has often been permitted to cause damage to the workpiece before being extinguished. Where direct current arcing protection circuits have been provided in the past, they have been inefficient in that they do not distinguish between direct current arcing which clears itself within the space of a normal cutting arc or spark and those which persist after the normal cutting cycle has been completed.